1. Field of the Invention
This invention relates to a method for production of hydrogen, hydrocarbons, and other by-products, and particularly to the production of hydrogen, liquid fuels, and other chemical fractions from catalytic processing of bio-oil.
2. Description of the Related Art
Hydrogen is an important feedstock for chemical manufacture and as a clean fuel in combustion engines and in fuel cells. Synthetic routes for commercial production of hydrogen have included catalytic steam reforming of C1-4 hydrocarbons such as methane, ethane, butane, and the like; natural gas; liquefied petroleum gas (LPG); naphtha; and the like; alternatively, hydrogen may be obtained by partial oxidation of heavy oil residues and coal gasification. However, because of the prospect of eventual depletion of global petroleum reserves and accompanying high prices, development of alternative sources of hydrogen from renewable sources is desirable. One potential renewable source of petroleum derived products is bio-based matter, such as agricultural and forestry products. Use of bio-based products may potentially counteract, at least in part, the problems associated with depletion of the petroleum supply.
One bio-based product is bio-oil. Bio-oil is the condensed liquid oxygenated hydrocarbon by-product of the fast pyrolysis of biomass, and in particular, biomass from agricultural and forest product residue. During pyrolysis, the biomass is heated to moderate temperatures (450 to 650° C.) in the absence of any externally supplied oxygen. The vapors formed on heating of the biomass condensed quickly to provide bio-oil as a liquid. Bio-oil is a complex mixture of various compounds including water, guaiacols, catechols, syringols, vanillins, furancarboxaldehydes, and carboxylic acids including acetic acid, formic acid, and other carboxylic acids [Mohan, D., Pittman, C. U. and Steele, P. H., “Pyrolysis of Wood/Biomass for Bio-oil: A Critical Review,” Energy & Fuels, 2006, vol. 20, pp. 848-889]. Bio-oil derived from fast pyrolysis of wood has an energy density about five times that of green wood, but is insoluble in hydrocarbon solvent and is acidic (with a pH of about 2 to about 3), is highly viscous, and the presence of oxygen containing compounds makes bio-oil thermally unstable. In addition, the high oxygen content of bio-oil also gives it a low energy density per unit volume or mass. For primarily these reasons, use of bio-oil as a fuel (e.g., gasoline or a heavy fuel oil such as diesel) or fuel additive is currently not feasible, and to be able to use bio-oil as liquid fuel it is necessary to convert it to a higher energy density, higher stability form. A representative comparison of composition and physical properties of bio-oil and heavy fuel oil is depicted in Table 1, below (reproduced from Czernik S. and Bridgewater A. V., “Overview of Applications of Biomass Fast Pyrolysis Oil”, Energy & Fuels, 2004, 18, pp. 590-598).
TABLE 1Bio-oilHeavy fuel oilPhysical propertyMoisture content (wt %)15-300.1pH2-3—Specific gravity1.20.94Elemental composition (wt %)C54-5885H5.5-7.011O35-401.0N  0-0.20.3Ash  0-0.20.1High Heat Value (HHV; MJ/Kg*)16-1940Viscosity (at 50° C. in cP) 40-100180Solids content (wt %)0.2-1  1Distillation residue (wt %)up to 501*Note:units are in megajoules per kilogram (MJ/Kg).**Note:viscosity is reported in centipoise (cP).
To make bio-oil compatible with or similar to the conventional liquid fuels it is first necessary to deoxygenate it. Two main routes to achieve this are hydrotreating and catalytic cracking [Czernik, Id.]. In hydrotreating, oxygen is removed in the form of water in the presence of a catalyst at high temperature and high hydrogen pressure. Maggi and Delmon [Maggi, R. and Delmon, B., “A Review of Catalytic Hydrotreating Processes for the Upgrading of Liquids Produced by Flash Pyrolysis”, in Hydrotreatment and Hydroprocessing of Oil Fractions, Froment, G. F., Delmon, B. and Grange, P. (Eds.), 1997, Elsevier Science B. V.] and Elliott [Elliott, D. C., Historical Developments in Hydroprocessing Bio-oils, Energy & Fuels, 2007,21, pp. 1792-1815] have reviewed the catalytic hydrotreating of bio-oil. In catalytic cracking, bio-oil has been passed over an acidic zeolite catalyst at high temperature (e.g. 450° C.) and atmospheric pressure. Simultaneous dehydration and decarboxylation reactions occur, and oxygen is removed in the form of H2O, CO and CO2 [Czernik and Bridgwater, Id.].
Elliott and Baker [Elliott, D. C. and Baker, E, G., “Biomass Liquefaction Product Analysis and Upgrading”, Comptes Rendus de l'Atelier de Travail sur la Liquidfaction de la Biomasse, Report 23 130, NRCC: Sherbrooke, Quebec, Canada, Sep. 29-30, 1983, pp. 176-183] report hydrotreating bio-oil over a sulfided Co—Mo catalyst at 355° C. and 2,000 psi (13.8 MPa) with a liquid hourly space velocity (LHSV) of 0.35. As defined herein, LHSV which is generally expressed as v/v/h, g/g/h, or as h−1, is the ratio of the hourly volume (or mass) of oil processed to the volume (or mass) of catalyst, and is a measure of the residence time of the liquid reactants in reactors, typically cylindrical reactors. An LHSV of 0.1 to 0.5 is typically used for vacuum residue feedstocks. Hydrogen consumption was found for the process to be 127 L/L of bio-oil, and a relatively low yield of 23% by mass was obtained for the liquid product (deoxygenated bio-oil). In addition, the catalyst bed and catalyst were plugged by heavy tar-like material (i.e., “coked), effectively blocking the active portions of the catalyst and preventing further catalytic cycling.
Elliott and Baker [Elliott, D. C. and Baker, E. G., “Process for Upgrading Biomass Pyrolyzates,” U.S. Pat. No. 4,795,841, issued Jan. 3, 1989] further developed a two-step process for upgrading bio-oil using sulfided Co—Mo as the catalyst for both steps. In the process, bio-oil was initially subjected to mild hydrotreating at 300° C. to make a stabilized product. The stabilized product was then subjected to further hydrocracking at 350° C. and 2,000 psi (13.8 MPa). A relatively low LHSV of 0.07 volume of oil/volume of catalyst-h is used in the second step. About 75 wt % of the carbon is converted to an oil phase containing 2.3 wt % oxygen, with an overall hydrogen consumption of about 457 L/L of oil produced.
Aqueous-phase reforming (APR) of biomass-derived hydrocarbons is a novel process developed by Cortright et al. [Cortright, R. D., Davda, R. R. and Dumesic, J. A., “Hydrogen from Catalytic Reforming of Biomass-derived Hydrocarbons in Liquid Water,” Nature, 2002, p. 418] to produce hydrogen by a low temperature (e.g., about 500K, or 228° C.) catalytic reforming of biomass-derived oxygenated compounds such as glucose, sorbitol, and the like, where platinum on alumina (Pt/Al2O3) is used as catalyst. For example, reforming of sorbitol to H2 and CO2 is described by the following balanced stoichiometric equation (1):C6H14O6(l)+6H2O (l)⇄13H2+6CO2  (1)where conversion to a gas phase fraction is higher at 538K than that at 498K. At 538K, the % C in the gas phase effluent is 84% (compared to 50%C at 498K), and 90% C (compared to 61% C at 498K) as obtained for reforming of glucose and sorbitol, respectively. The gas phase contains H2, CO2, and C1-6 alkanes in varying amounts.
The hydrogen production in the method of Cortright et al. is somewhat low compared with the percent carbon recovery, as measured by the hydrogen selectivity. Hydrogen selectivity is defined in equation (2) as:H2 Selectivity=(molecules H2 produced/C atoms in gas phase)*(1/RR)*100  (2)where RR is the H2/CO2 Reforming Ratio, corresponding to 13/6 and 2 for sorbitol and glucose, respectively, and is a function of conversion of the feedstock from the solution to gas phase. For example, hydrogen selectivity by the method of Cortright is 50% and 36% for glucose at 498K and 538K respectively, and 66% and 46% for sorbitol 498K and 538K, respectively. However, application of such reformation reactions has generally been confined to model compounds and not to actual unrefined bio-oil with its accompanying complex lignin-derived feed and resulting char formation.
In addition, International Patent Application Publication No. WO 2008/069830 discloses aqueous phase reforming of various purified or semi-purified polyol starting materials, to provide hydrogen. Hence, the feed in this application is appears limited to polyols which are converted in the aqueous phase reforming step, and does not disclose the use of a functionally complex starting material in the feed, such as fractionated bio-oil.
Accordingly, there still remains a need in the art for a method of efficient production of fuels, including hydrogen and hydrocarbons, derived from bio-oils.